Acoustic noise reduction in power supply inductors

ABSTRACT

Embodiments of the present invention provide an apparatus that reduces an audible noise produced in a power supply. The apparatus includes: (1) a housing; (2) an inductor coil formed from a coil of wire enclosed in the housing; (3) a set of wires that are coupled from the inductor coil to the outside of the housing through corresponding apertures in the housing, comprising electrical leads for the inductor coil; and (4) a predetermined amount of adhesive in the apertures that bonds the wires to the housing to reduce an audible noise produced when the current through the inductor coil is cycled quickly.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to electronic circuits andpower supplies. More specifically, embodiments of the present inventionrelate to techniques for reducing acoustic noise from power supplyinductors.

2. Related Art

Many modern computer systems operate under strict power consumptionlimitations. In order to meet these limitations, some computer systemssupport one or more low-power modes in which some of the computer'scomponents operate using less power or are disabled. For example, duringa low-power power mode, the computer system's hard drives can bestopped, the display can be deactivated, and/or the CPU clock can beslowed down.

When operating in full-power mode, the computer system draws currentfrom a power supply according to the load on the computer system. Forexample, FIG. 1A presents a graph illustrating a current-flow patternduring full-power mode. As can be seen from FIG. 1A, the computer systemdraws different levels of power for different loads. For example, when auser loads a program from disk into memory, the disk, the memory, andthe CPU are all activated. Hence, power usage increases, which increasesthe current drawn from the power supply. When the computer systemsubsequently finishes loading the program from disk, there is acorresponding decrease in the current drawn from the power supply.

When operating in low-power mode, the computer system can disable allbut a minimal subset of computer system components. For example, thelow-power mode may be a “sleep mode,” wherein all components aredeactivated except a hardware monitor that is designed to wake thecomputer system upon receiving a communication from a peripheral (e.g.,a keystroke or mouse movement). During the low-power mode, the computersystem draws a small fraction of the power drawn during full-power mode.For example, FIG. 1B presents a graph illustrating a current-flowpattern during a low-power mode.

Some computer systems support a hybrid mode, which limits powerconsumption by dynamically disabling and re-enabling computer systemcomponents and features as they are used. Although the components andfeatures are sometimes disabled in the hybrid mode, the computer systemappears to be fully functional. For example, in some hybrid modes, thecomputer system may slow down the CPU clock when a user is notperforming operations that require the full CPU power. In some systems,during the hybrid mode the computer system cycles between a specializedlow-power mode and full-power mode at every opportunity (e.g., betweenkeystrokes). For example, FIG. 1C presents a graph illustrating acurrent-flow pattern during a hybrid low-power/full-power mode. As shownin FIG. 1C, the computer system is subject to significant current swingsduring the hybrid mode (i.e., high di/dt).

Unfortunately, some computer systems include parts in the power supplythat perform inadequately during such hybrid modes. For example, in somepower supplies, an inductor will produce a clearly audible whine causedby the high di/dt when cycling back and forth between low-power mode andfull-power mode. Because there are often limitations on the noise thatcomputer systems (particularly laptops) may emit, an audible whine fromthe power supply may be unacceptable.

Hence, what is needed is a power supply for a computer system withoutthe above-described problem.

SUMMARY

Embodiments of the present invention provide an apparatus that reducesan audible noise produced in a power supply. The apparatus includes: (1)a casing; (2) an inductor coil formed from a coil of wire enclosed inthe casing; (3) a set of wires that are coupled from the inductor coilto the outside of the casing through corresponding apertures in thecasing comprising electrical leads for the inductor coil; and (4) apredetermined amount of adhesive in the apertures that bonds the wiresto the casing to reduce an audible noise produced when the currentthrough the inductor coil is cycled quickly.

In some embodiments, the set of wires extend along the casing from thecorresponding set of apertures and under the casing alongside an outsidesurface of the casing forming “J” leads for coupling the inductor coilto an electrical circuit.

In some embodiments, a mechanical mount is coupled to the outside of thecasing on an opposite side of the casing from the set of apertures.

In some embodiments, the casing is formed by press-fitting metal dustpowder around the inductor coil.

Embodiments of the present invention provide a method for manufacturingan inductor for reducing an audible noise in an electrical circuit.During the process, an inductor coil is first wound from a segment ofwire. Next, the wound inductor coil is enclosed in metal dust powder.The metal dust powder is then press-fit into a casing for the inductor,wherein a set of wires are coupled from the inductor coil to the outsideof the casing through a corresponding set of apertures in the casing (toserve as electrical leads for the inductor coil). Next, a predeterminedamount of adhesive is placed in the apertures to bond the wires to thecasing to reduce an audible noise produced when the current through thecircuit element is cycled quickly.

Embodiments of the present invention provide a computer system forreducing an audible noise produced in a power supply. The computersystem includes a processor and a power supply that provides power tothe processor. The power system includes: (1) a casing; (2) an inductorcoil formed from a coil of wire enclosed in the casing; (3) a set ofwires that are coupled from the inductor coil to the outside of thecasing through corresponding apertures in the casing, wherein the wiresform electrical leads for the inductor coil; and (4) a predeterminedamount of adhesive in the apertures that bonds the wires to the casingto reduce an audible noise produced when the current through theinductor coil is cycled quickly.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A presents a graph illustrating a current-flow pattern during afull-power mode in a computer system.

FIG. 1B presents a graph illustrating a current-flow pattern during alow-power mode in a computer system.

FIG. 1C presents a graph illustrating a current-flow pattern during ahybrid low-power/full-power mode.

FIG. 2A presents a block diagram of a computer system in accordance withembodiments of the present invention.

FIG. 2B presents a block diagram of a power supply in a computer systemin accordance with embodiments of the present invention.

FIG. 2C presents a circuit diagram illustrating a buck converter circuitin accordance with embodiments of the present invention.

FIG. 3A presents a front view of an inductor in accordance withembodiments of the present invention.

FIG. 3B presents a side view of an inductor in accordance withembodiments of the present invention.

FIG. 3C presents an isometric view of an inductor in accordance withembodiments of the present invention.

FIG. 4A presents a front view of an inductor with a casing partiallycut-away to reveal the inductor coil in accordance with embodiments ofthe present invention.

FIG. 4B presents a side view of an inductor with a casing partiallycut-away to reveal the inductor coil in accordance with embodiments ofthe present invention.

FIG. 4C presents a top view of an inductor with a casing partiallycut-away to reveal the inductor coil in accordance with embodiments ofthe present invention.

FIG. 5 presents a flowchart illustrating a method of manufacturing aninductor in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notlimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the claims.

Computer System

FIG. 2A presents a block diagram of a computer system 200 in accordancewith embodiments of the present invention. Computer system 200 includesprocessor 202, memory 204, and mass-storage device 206. Computer system200 also includes power supply 208, which supplies electrical power toprocessor 202, memory 204, mass-storage device 206, and other componentsin computer system 200 (not shown)

In some embodiments of the present invention, computer system 200 is ageneral-purpose computer system that supports low-power modes, includingsleep, idle, and/or standby modes. During these low-power modes, some orall of the functions and/or components of computer system 200 are sloweddown or disabled to conserve power. For example, when operating in alow-power mode, computer system 200 may slow down or disable processor202, memory 204, mass-storage device 206, and/or other devices such asmonitors and peripheral devices (not shown).

In embodiments of the present invention, computer system 200 alsosupports one or more “hybrid” modes in which computer system 200 appearsto be in full-power mode, but instead dynamically switches from afull-power mode to one or more special low-power modes as conditionspermit. For example, computer system 200 may slow down the CPU clockand/or other system clocks whenever the load on the CPU and othercomponents is low, but may restore the CPU clock and/or other systemclocks when the load increases. In some embodiments, computer system 200can enter and exit a special low-power mode very rapidly, facilitating anearly continuous switch between the modes. For example, when a user isediting a document, computer system 200 may generally operate infull-power mode, but as often as between keystrokes computer system 200may enter the specialized low-power mode.

In FIG. 2A, processor 202 is a central processing unit (CPU) thatprocesses instructions for computer system 200. For example, processor202 can be a microprocessor, a device controller, or other type ofcomputational engine. Memory 204 is volatile memory that storesinstructions and data for processor 202 during operation of computersystem 200. For example, memory 204 can include DRAM, SDRAM, or anotherform of volatile memory. Mass-storage device 206 is a non-volatilestorage device that stores instructions and data for processor 202. Forexample, mass-storage device 206 can be a hard disk drive, a flashmemory, an optical drive, or another non-volatile storage device.

Note that although we describe embodiments of the present inventionusing computer system 200, alternative embodiments can be used withinother types of computing systems. Moreover, embodiments of the presentinvention are operable in any type of electronic device wherein acircuit element produces an audible noise caused by significant di/dt.

Power Supply

FIG. 2B presents a block diagram of a power supply in computer system200 in accordance with embodiments of the present invention. The powersupply includes adaptor 210, charger 212, and a set of DC/DC converters214 and 216 (i.e., voltage regulators).

Adapter 210 converts an AC signal from a power source (e.g., a common120 VAC electrical outlet) to a 16.5 VDC signal which is in turnconverted by charger 212 into a 12.6 VDC signal. The 12.6 VDC signal isthen used as an input for DC/DC converters 214. The 12.6 VDC signal canalso be used to charge a battery (not shown) if there is a batterypresent in the system.

FIG. 2C presents a circuit diagram illustrating a buck converter circuit220 in accordance with embodiments of the present invention. Buckconverter circuit 220 is a switched-mode step-down DC-to-DC converter.Note that charger 212 includes a buck converter circuit 220.

Buck converter circuit includes inductor 222, capacitors 224 and 230,and switching elements 226 and 228. The operation of the circuitelements in the buck circuit is known in the art, hence a more detaileddescription is not provided. Note that in some embodiments of thepresent invention, both switching element 226 and 228 are transistors.However, in alternative embodiments, switching element 226 is atransistor while switching element 228 is a diode or another suchcircuit element.

Inductor

FIG. 3A-3C present front, side, and isometric external views of aninductor 222 in accordance with embodiments of the present invention.Inductor 222 includes casing 302, electrical leads 306, and mechanicalmount 304.

In some embodiments of the present invention, casing 302 is formed frompress-fit metal dust powder. In these embodiments, inductor coil 400(see FIG. 4) is formed from a segment of wire. Inductor coil 400 is thenenclosed in metal dust powder, which is pressed into the final shape ofcasing 302. When pressing the metal dust powder around inductor coil400, a pressure of several tons of force per square inch is used.Although there are multiple forms of metal dust powder that may be usedto form casing 302, forming an inductor casing from metal dust powder isknown in the art and is therefore not described in more detail. Notethat although we describe embodiments of the present invention that usepress-fitting to form the casing, alternative embodiments use sinteringor other techniques to form the casing from the metal dust powder.

In some embodiments, casing 302 is a small-outline j-lead (SOJ) packagefor surface-mounting inductor 222. Hence, as shown in FIGS. 3A-3C,electrical leads 306 extend out of an aperture in the side of casing302, then run alongside casing 302, and under casing 302 as shown inFIG. 3B (i.e., the leads appear as a “J”). In addition, mechanical mount304 is bonded to the outside of casing 302 on the opposite side ofcasing 302 from electrical leads 306. Mechanical mount 304 runsalongside casing 302, and under casing 302 as shown in FIG. 3B (i.e.,also appearing as a “J”). Note that although we describe embodiments ofthe present invention using the SOJ package, in alternative embodiments,casing 302 is in another packaging format.

When placed in an electrical circuit, inductor 222 is mounted by bonding(e.g., soldering) electrical leads 306 and mechanical mount 304 to amounting surface. In some embodiments of the present invention,mechanical mount 304 has no electrical function and serves only as athird mounting point for inductor 222 in order to provide mechanicalstability.

Inductor 222 also includes adhesive 308 on electrical leads 306. Duringmanufacture, adhesive 308, initially liquid, is placed in aperture 402(see FIG. 4B) from which electrical leads 306 extend out of casing 302.Adhesive 308 then sets, bonding the electrical leads 306 to one or morewalls of aperture 402. By bonding electrical leads 306 to casing 302 inthis way, a significant reduction in acoustic noise is achieved.

Adhesive 308 can be any adhesive used to bond electrical parts to oneanother. Such adhesives are known in the art. In some embodiments of thepresent invention, the adhesive is Chemiseal E-1358B from the ChemitechInc. of Tokyo, Japan.

FIGS. 4A-4C present front, side, and top partially cut-away views ofinductor 222 in accordance with embodiments of the present invention. Inthe front view in FIG. 4A, inductor coil 400 can be seen within casing302 (although inductor coil 400 is partially obscured by electricalleads 306).

In the side view in FIG. 4B, an electrical lead 306 can be seenextending from inductor coil 400 out of aperture 402 in casing 302 andaround casing 302 in the “J”-shape described above. Adhesive 308 bondselectrical lead 306 to one or more walls of aperture 402 in casing 302.Bonding electrical leads 306 to the walls of aperture 402 stabilizeselectrical leads 306, which minimizes the movement of electrical leads306 when inductor 222 experiences high di/dt during the hybrid mode.Minimizing the movement of electrical leads 306 reduces the acousticnoise that might otherwise be produced by inductor 222.

In the top view in FIG. 4C, inductor coil 400's circular shape isvisible with electrical leads extending from inductor coil out ofaperture 402 in casing 302. Also shown is adhesive 308, which bondselectrical leads 306 within aperture 402.

Note that in some embodiments of the present invention, casing 302 maynot include aperture 402. In these embodiments, electrical leads 306extend directly out of the side of casing 302 and adhesive 308 can be adrop on the surface of casing 302 that surrounds electrical lead 306(and bonds electrical lead 306 to casing 302).

Manufacturing Process

FIG. 5 presents a flowchart illustrating a method of manufacturing aninductor in accordance with embodiments of the present invention. Theprocess starts when inductor coil 400 is wound from a segment of wire(step 500). Inductor coil 400 is then enclosed by metal dust powder,which is press-fit into the final shape of casing 302 (step 502). Whenstep 502 is complete, electrical leads 306 extend from inductor coil 400within casing 302 out of aperture 402 and around casing 302 in the“J”-shape described above.

Next, adhesive 308 is placed in aperture 402 in order to bond electricalleads 306 to casing 302 (step 504).

Alternative Embodiments

In some embodiments of the present invention, inductor 222 is entirelycovered with adhesive 308. In these embodiments, as with embodimentswhere the adhesive is only placed in aperture 402, adhesive 308 bondselectrical leads 306 to casing 302 (as described above). Theseembodiments incur the cost of the additional adhesive to avoid themanufacturing step of precisely placing the correct amount of adhesivedirectly in apertures 402.

In some embodiments, inductor 222 is mounted by adhesively bonding thecenter of casing 302 to a mounting surface along with soldering orotherwise bonding electrical leads 306 and mechanical mount 304 to themounting surface. By adhesively bonding the center of casing 302,acoustic noise is further reduced.

The foregoing descriptions of embodiments of the present invention havebeen presented only for purposes of illustration and description. Theyare not intended to be exhaustive or to limit the present invention tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention. The scope ofthe present invention is defined by the appended claims.

1. A circuit element, comprising: a casing; an inductor coil formed froma coil of wire enclosed in the casing; a set of wires that are coupledfrom the inductor coil to the outside of the casing throughcorresponding apertures in the casing, wherein the wires compriseelectrical leads for the inductor coil; and a predetermined amount ofadhesive in the apertures that bonds the wires to the casing to reducean audible noise produced when the current through the inductor coil iscycled quickly.
 2. The circuit element of claim 1, wherein the set ofwires extend along the casing from the corresponding set of aperturesand under the casing alongside an outside surface of the casing forming“J” leads for coupling the inductor coil to an electrical circuit. 3.The circuit element of claim 1, further comprising a mechanical mountcoupled to the outside of the casing on an opposite side of the casingfrom the set of apertures.
 4. The circuit element of claim 1, whereinthe casing is formed by press-fitting metal dust powder around theinductor coil.
 5. The circuit element of claim 1, wherein the casing isformed by shaping and sintering metal dust powder around the inductorcoil.
 6. The circuit element of claim 1, wherein the adhesive isChemiseal E-1358B or another adhesive used to bond electricalcomponents.
 7. The circuit element of claim 1, wherein the adhesiveincludes a material other than solder.
 8. The circuit element of claim1, wherein the adhesive is placed in the apertures after the coil ofwire is enclosed in the casing.
 9. A method for manufacturing aninductor, comprising: winding an inductor coil from a segment of wire;encasing the inductor coil in a casing, wherein a set of wires arecoupled from the inductor coil to the outside of the casing through acorresponding set of apertures in the casing to form electrical leadsfor the inductor coil; and placing a predetermined amount of adhesive inthe apertures to bond the wires to the casing to reduce an audible noiseproduced when the current through the circuit element is cycled quickly.10. The method of claim 9, wherein encasing the inductor coil in thecasing involves enclosing the inductor coil in metal dust powder andpress-fitting or sintering the metal dust powder.
 11. The method ofclaim 9, wherein the adhesive is Chemiseal E-1358B or another adhesiveused to bond electrical components.
 12. The method of claim 9, whereinplacing the adhesive in the apertures involves placing the adhesive inthe apertures after encasing the inductor coil in the casing.